1. Field of the Invention
The present invention relates to detectors for detecting the presence of metal and hard objects in crop material being transported along a crop feed path in a forage harvester. More particularly, the invention relates to the mounting of the detectors in a fixed position on a common support inside a hollow feed roll comprising a part of the crop feed mechanism of the harvester.
2. The Prior Art
The presence of foreign objects in harvested crop material has long been recognized as a problem, particularly where the crop material is destined for use as an animal feed. The foreign objects, such as pieces of metal, stones and other foreign objects may be ingested by the animals. In addition, the foreign objects may damage the cutterhead of the harvester. Therefore, it is desirable to be able to sense the presence of foreign objects in the crop material passing through the harvesting machine, and stop the transport of the crop material when a foreign object is sensed to thereby prevent the foreign object from reaching the cutterhead.
The foreign objects occurring in crop material may be metal objects, or stones and other hard objects. Generally speaking, two general types of foreign object detectors are known in the art. One type, generally referred to as metal detectors, detects metal objects and stops the crop feed mechanism upon detection of such an object. U.S. Pat. No. 4,433,528 to Bohman discloses such a metal detector mounted in a hollow feed roll comprising part of the feed mechanism of a forage harvester.
The second type of detector, generally referred to as a stone detector, detects stones and other hard objects including metal objects. Stone detectors may take many forms and be located at various positions in the harvester. U.S. Pat. No. 4,353,199 to Chow et al. discloses a stone detector which is mounted inside a hollow feed roll of a harvesting machine for detecting stones and other hard objects. However, the detector in this device senses mechanical vibrations set up in the feed roll as a result of the impacts of hard objects on the feed roll. This requires that the detector be mounted on, and rotate with, the feed roll thereby requiring a rotary coupling or slip ring in order to convey output signals from the detector to the circuits external of the feed roll which stop the feed mechanism. Furthermore, this arrangement requires that the feed roll be shock mounted so as to isolate the feed roll (and thus the detector) from machine generated vibrations.
Summary of the Invention
An object of the present invention is to provide, in a harvesting machine having a crop feed mechanism including at least one hollow rotatable feed roll for feeding a crop material to a rotating cutterhead, a first sensor for sensing metal objects in the crop material and a second sensor for sensing hard objects in the crop material, both sensors being mounted on a common fixed support member inside the hollow feed roll and producing output signals to stop the crop feed mechanism upon detection of a metal or hard object in the crop material. The second sensor is preferably a thin film microphone for sensing air-borne sound waves inside the feed roll resulting from impacts of hard objects on the exterior of the feed roll. The fixed support member is a non-rotatable shaft about which the feed roll rotates.
In one embodiment, the first sensor is located within a housing supported by the fixed shaft and the second sensor is mounted on the outside of the housing, a vibration-absorbing pad being provided to isolate the second sensor from vibrations occurring in the housing.
In a second embodiment, the second sensor is mounted on a printed circuit board supported by a member attached to the fixed shaft, a vibration-absorbing pad being provided between the printed circuit board and the member.
Other objects of the invention and its mode of operation will become apparent upon consideration of the following description and the accompanying drawings.